The present invention relates to an improved light source which can emit in one direction a light beam composed of composite spectra from two types of light emitters enclosed within an envelope.
In Japanese Utility Model Registration No. 1,350,774 (Application No. 115714/1976), filed in the name of Hamamatsu TV Co., Ltd., this type of lamp was disclosed, and such a lamp has already been highly appreciated by the users.
Referring to FIGS. 1, 2 and 3, the configuration of this prior type of lamp will be described to provide a basis for explaining the problems which have been encountered in this type of lamp.
FIG. 1 shows a perspective view of a composite light source built in accordance with the above-referred to prior art.
FIG. 2 sshows a sectional view of the composite light source shown in FIG. 1.
FIG. 3 shows an enlarged sectional view of the main portion of the composite light source shown in FIGS. 1 and 2.
As shown in FIGS. 1 and 2, sealed envelope 1 is almost cylindrical and has a light emitting window 2 on a portion of the surface thereof.
Light emitting window 2 is made of quartz which does not absorb UV rays.
A shielding box 3 made of metal plates is located within sealed envelope 1. It is supported by a metal rod fastened to the stem at the bottom of sealed envelope 1 in the same manner as the electrodes.
The space enclosed within shielding box 3 is divided into a plurality of sub-spaces by separation walls made of metal plates, as shown in FIG. 2, and aperture 9 is provided for emitting light onto the surface located against the quartz window 2. Cathode 4 is provided on the upper side of the first space wherein the aperture 9 is provided. Cathode 4 is cylindrical, and within it a heater is formed.
An anode having an aperture 7 is provided at the center in the second space of the shielding box 3.
A wall separating the second space from the first space extends to the anode 5, and aperture 8 with a small diameter is provided at the top thereof.
A tungsten lamp 6 having a filament 10 is provided in the third space.
An aperture 23 is provided on the wall separating the third space from the second space.
Light emitting window 2 made of quartz, aperture 9 in shielding box 3, aperture 8, aperturre 7 of anode 5, and filament 10 are sequentially arranged in line at their centers.
Deuterium gas is introduced into sealed envelope 1 with light emitting window 2 made of quartz.
An appropriate voltage is applied to anode 5 with respect to cathode 4. An arc discharge occurring in the deuterium gas atmosphere can partly pass through the narrow channel formed by the aperture 8, and this causes a bright spot to occur in an area near aperture 8. When power is supplied to the tungsten lamp 6, filament 10 is brightened at high brightness and the energy component arriving at the aperture 8, among those emitted from filament 10, is projected in the forward direction.
One of the following three types of light sources can be obtained by simultaneously or selectively specifying light from an arc discharge occurring in the deuterium gas atmosphere or light from the tungsten lamp 6.
(1) Light source with a spectra covering the 190 nm to 3000 nm range, PA0 (2) Light source providing a UV ray (due to an arc discharge in the deuterium gas atmosphere) with the main energy covering the 190 nm to 390 nm range, PA0 (3) Light source (by tungsten lamp) emitting visible and infra red rays.
The light source in the above-mentioned structure can be used to obtain a bright spot emitting visible and infra red rays as well as UV rays from an arc discharge. The tungsten lamp thus emits light at very low efficiency in the above-mentioned lamp.
Part of the energy emitted from filament 10, which is not limited by aperture 8, can be used as a light source but that which is limited by the aperture cannot be used. Excessive power is required to heat filament 10 within tungsten lamp 6 if the same amount of energy as that obtained by the light source (1) utilizing an arc discharge is required. Part of the energy obtained by filament 10, for instance, 10 to 30 watts remain in the lamp and it elevates the filament temperature.
Tungsten lamp 6 is housed within sealed envelope 1 and energy stored in filament 10 cannot easily be removed. This elevates the temperature within sealed envelope 1. If the tungsten lamp 6 is continuously used for a long period of time, the temperature of anode 5 becomes several hundred degrees Celsius. Electrons striking anode 5 under those conditions can evaporate anode surface materials. Tungsten lamp 6 is located near anode 5 so as to increase the efficient with which the light beam is utilized. The evaporated materials can easily be deposited onto the transparent side wall within tungsten lamp 6 thereby making the side wall opaque. The evaporated materials can easily be deposited onto window 2 made of quartz, and this makes the window opaque. The radiation intensity obtained by tungsten lamp 6 thus decreases with time as shown in curve a of FIG. 8.
The objective of the present invention is to provide an improved composite light source which can eliminate variations in the light intensity with time.